ABSTRACT

This report provides an overview of the stock assessment, harvest strategy, and regulations effective for the 2023 Northern Southeast Inside (NSEI) sablefish (Anoplopoma fimbria) commercial fishery. The NSEI sablefish commercial fishery is scheduled to open August 15 and close November 15 and open to both longline and pot gear. The 2023 NSEI sablefish commercial fishery annual harvest objective is 1,395,686 round pounds and is based on decrements from an acceptable biological catch of 1,573,109 round pounds. The annual harvest objective is allocated to 73 limited entry Commercial Fisheries Entry Commission C61A permits through an equal quota share (EQS) system, resulting in a 2023 EQS of 19,121 round pounds for each permit holder.

Key words: sablefish, black cod, Anoplopoma fimbria, stock assessment, annual harvest objective, AHO, catch per unit effort, CPUE, Northern Southeast, Chatham Strait, NSEI, mark–recapture, tagging


INTRODUCTION

The Alaska Department of Fish and Game (ADF&G) evaluates stock status and establishes the Northern Southeast Inside (NSEI) acceptable biological catch (ABC) and subsequent annual harvest objective (AHO). The NSEI Subdistrict management area (Figure 1) consists of all waters as defined in 5 AAC 28.105(a)(2).

The recommended 2023 allowable biological catch (ABC) is 1,573,109 round pounds (\(F_{ABC}\) = 0.063), a 9% increase from the 2022 ABC (Table 1 and 2). After making decrements for sablefish mortalities in other fisheries, the 2023 NSEI Subdistrict commercial sablefish fishery annual harvest objective (AHO) is 1,395,686 round pounds (Table 1 and 3). There are 73 valid Commercial Fisheries Entry Commission (CFEC) permits for 2023, which is the same number as 2022. The individual equal quota share (EQS) is 19,121 round pounds, a 13% increase from the 2022 EQS of 16,899 round pounds (Table 1).

Several advancements to the stock assessment and statistical catch-at-age (SCAA) model were implemented for the 2023 NSEI sablefish assessment that improved the model’s ability to capture the dynamics of the stock. These advancements are:

  1. Fishery CPUE was fully standardized to correct for variability in fishing methods and practices (i.e, hook size, fishing depth, length of sets, location, etc.) to better detect underlying trends that reflect the abundance of fish available to the fishery. This involved recalculating fishery CPUE from the re-entered logbook data that was completed in 2020.
  2. Fishery selectivity in the SCAA was updated to the fixed values estimated in the federal sablefish fishery assessment (Goethel et al. 2022). Selectivity in the time period prior to implementation of the IFQ fishery in 1995 changed significantly from the last assessment such that the curve is substantially less steep indicating that fewer, smaller fish were being selected for in the pre-IFQ fishery than previously estimated. This has the effect of increasing the apparent size of the population during that time period and thus reducing stock status today. The model is now capable of estimating fishery selectivity within the model, but the estimated selectivity curves are suspect and further work needs to be done before this version of the model is implemented.
  3. Survey selectivity was switched from the fixed values borrowed from the federal domestic longline survey values to being freely estimated in the SCAA model, thus being a more accurate reflection of the NSEI longline survey. This involved adding a second time block to reflect the switch from an unstandardized survey prior to 2000 and the fully standardized fishery that began in 2000.
  4. The recruitment process is now modelled using random effects which allows for the estimation of variability, \(\sigma_R\). Prior to this assessment, \(\sigma_R\) had been fixed at the assumed federal assessment value of 1.2.
  5. The data weighting of the model was changed to reflect best practices in SCAA modelling. This involved tuning the age and length compositional data to adjust the effective sample sizes using McAllister and Ianelli (1997) and removing the fixed weights that had been applied to the abundance indices (mark-recapture estimates, longline survey CPUE and longline fishery CPUE). The variance of the longline survey was changed from assumed values to the true estimates. The fishery CPUE and mark-recapture variance was kept at the inflated and fixed values to allow for the extra uncertainty in these indices owing to the unrecorded releases of fish that are permitted in the fishery and unquantified biases in the mark-recapture project.

With these changes, the recommended 2023 ABC is 1,573,109 round lb (\(F_{ABC}\) = 0.063), a 9% increase from the 2022 ABC. The ABC was calculated as an average of the base model and the new model (v23) to balance the clear increase in biomass with the uncertainty about stock status evident in comparing the base and v23 models. The increase in the ABC is attributed to the continued growth and maturation of the strong recruitment events since 2015, highlighted by recruitment in 2018 (the 2016 year class) which is the highest recruitment since 1979. The dominant 2016 year class is now 50% mature and will comprise 27% of the biomass. All three abundance estimates are elevated from recent years with the highest abundance estimate on record from the mark-recapture project, the third sustained year of high CPUE in the longline survey and increasing CPUE in the longline fishery. However, the lower stock status estimated in the new model results in less of an increase than was present in using the 2022 model (the base model). The recommended ABC is thus an average of the recommended ABC from the base model used in past assessments and the new model v23 used in this assessment. Fishery catch and ex-vessel value remain depressed from historical levels, but have increased since 2022 as the 2013-2018 year classes reach marketable sizes and are being landed and retained in the fishery (Figure 2). Though recent high catch rates of small sablefish across multiple geographic areas signal increasing trends for sablefish stocks (Goethel et al. 2022), the department maintains a precautionary approach to setting harvest limits. Estimates from the 2022 stock assessment suggest sablefish spawning stock biomass remains at suppressed levels compared to the 1980s and 1990s.

The ABC determination process uses a statistical catch-at-age model, which was first implemented in 2020. The model reduces the reliance on the annual mark-recapture project to estimate recruitment, abundance, and spawning stock biomass of NSEI sablefish by integrating multiple indices of abundance and biological data (e.g., catch, mark-recapture abundance estimates, longline survey and fishery CPUE, longline survey length and age compositions). As in previous years, maximum ABC is defined by \(F_{50}\), the fishing mortality rate that reduces spawning biomass to 50% of equilibrium unfished levels.

The process leading to the determination of the ABC, AHO, and EQS includes compiling fishery and survey data, running the stock assessment, and accounting for additional sources of mortality through decrements. Although the ABC is determined prior to the AHO and EQS, this report is organized to make management-related information accessible to stakeholders and improve documentation of the assessment process by organizing this report into the following sections:

  1. 2023 Sablefish Management Plan: details the decrements process leading to the AHO and EQS and effective regulations for the 2023 NSEI fishery.
  2. 2022 Sablefish Stock Assessment and 2023 ABC Determination: highlights stock assessment data inputs, methods, results, and subsequent analyses that informed the recommended ABC.


2023 SABLEFISH MANAGEMENT PLAN

ANNUAL HARVEST OBJECTIVE DETERMINATION

The 2023 AHO was determined by making the following decrements from the recommended ABC (1,573,109 round pounds, Tables 2 and 3):

  • estimated sablefish bycatch mortality in the commercial Pacific halibut fishery,
  • ADF&G longline survey removals,
  • sport fishery guided and unguided harvest,
  • mortality from fishery deadloss, and
  • subsistence and personal use harvest.

Bycatch mortality in the halibut fishery

Sablefish caught in NSEI during the Pacific halibut individual fishing quota fishery prior to the sablefish fishery season opening (August 15) must be released; however, because not all are expected to survive, bycatch mortality is estimated. Prior to 2003, a 50% bycatch morality rate was applied as bycatch sablefish were permitted to be retained as bait. In 2003, the Alaska Board of Fisheries disallowed retaining bycatch sablefish for bait, and a 25% bycatch mortality rate was assumed for all sablefish caught and released due to the larger hook size in the Pacific halibut fishery. Released sablefish bycatch is calculated as the product of the 3-year average of the sablefish to Pacific halibut ratio from the International Pacific Halibut Commission (IPHC) annual survey and the 3-year average of the Pacific halibut catch in areas greater than 99 fathoms in NSEI.

ADF&G longline survey removals

In 2022, no NSEI permit holders will participate in the NSEI longline survey due to budgetary instability and deficit given the low prices of sablefish in 2020 and 2021 (Tables 1 and ???). The survey removal decrement was determined by averaging the survey total harvest from the previous 3 years. Permit holders will likely resume survey participation in 2023.

Sport fish harvest (guided and unguided)

Sablefish sport fish preliminary harvest and release mortality from the guided and unguided sectors are estimated utilizing charter logbooks and the statewide harvest survey (Romberg et al. 2017). Estimates of harvested and released fish are based on the total number of fish and converted to weight using a 3-year average of fish sampled from the guided and unguided sectors. A 10% release mortality rate is applied to the sport fishery; this was based on the 11.7% estimated in Stachura et al. (2012) and modified to account for difference in gear type (rod and reel versus longline) and handling time.

Mortality from fishery deadloss

Deadloss mortality in the directed sablefish fishery was estimated by applying the percentage of dead sablefish (i.e., recorded as predated by sand fleas, sharks, hooking injury, or other cause of mortality) caught on the NSEI longline survey using the recent 3-year average, 0.85% (2020–2022), to the NSEI sablefish commercial AHO.

Personal use and subsistence harvest

A total of 772 personal use and subsistence sablefish permits were issued in 2022. Annual subsistence and personal use harvest of sablefish is estimated from these permits by adding the total number of retained sablefish reported to the proportion of released sablefish reported after applying a 16% discard mortality rate to released sablefish (Gilroy and Stewart 2013). The Pacific halibut fishery is assumed a reasonable proxy for sablefish because the fisheries utilize similar gear and frequently the same vessels and crew participate in both fisheries. Moreover, both species are considered hardy and do not experience barotrauma. The 2022 longline survey average weight (5.1 lb) was applied to this harvest to obtain a decrement total. In 2015, personal use harvest was limited to an annual limit of 50 fish per household. Since 2018, participants of the personal use fishery have been allowed to use pot gear with no more than 2 pots per permit and a maximum of 8 pots per vessel when 4 or more permit holders are on board the same vessel. Use of pot gear has continued to increase with 68% of permit holders fishing pots.


REGULATIONS

2022 Board of Fisheries Decisions

In March 2022, the Alaska Board of Fisheries adopted new regulations that will be enacted prior to or during the fishing season for the NSEI sablefish commercial fishery. An advisory announcement will be issued at a later date with more information. These new regulations include:

  • Full retention requirements and landing requirements using hook-and-line and pot gear for all species of rockfish including thornyhead rockfish.
  • Allowing pot gear as a legal gear type in addition to longline gear for the C61A permits, which is contingent upon the approval process through CFEC.
  • Pots must have at least two circular escape rings, with a minimum inside diameter of three and three-fourths inches, installed on opposing vertical or sloping walls of the pot.

Registration and logbook requirements

Fishermen must register prior to fishing [5 AAC 28.106 (b)] and keep a logbook during the fishery. Completed logbook pages must be attached to the ADF&G copy of the fish ticket at the time of delivery. Confidential envelopes for logbook pages may be requested when registering.

Permit holders will receive a personal quota share (PQS) tracking form at the time of registration. This form is used to record the total round weight landed for each delivery. Each permit holder must, upon request, provide the buyer with the total round weight of sablefish the permit holder has landed to date. The department requests that a copy of the completed PQS tracking form is included with the final fish ticket of the season for that permit.

Logbooks must include, by set, the date and time gear is set and retrieved, specific location of harvest by latitude and longitude for start and ending positions, hook spacing, amount of gear (number of hooks and skates) used, depth of set, estimated number or weight of the target species, and the estimated number or weight of bycatch by species. Permit holders must indicate for each set if the target species was sablefish or Pacific halibut and if there was any gear lost. A permit holder must retain all visibly injured or dead sablefish. Sablefish that are not visibly injured or dead may be released unharmed, and the permit holder must record in the logbook, by set, the number of live sablefish released [5 AAC 28.170(f)]. Permit holders must record release reason (e.g., fish are small) and whether their personal quota share has been met.

Tagged sablefish

Fishermen are requested to watch for tagged sablefish, record tag number(s), and attach tags directly in the logbook with the corresponding set information. All tags returned will receive a reward. Tag rewards include a t-shirt and entry into an annual drawing for one $1,000, two $500, and four $250 cash rewards. To qualify for entry in the annual drawing, ADF&G requires the following information: the tag, set location (latitude and longitude), date of capture of the fish, and the name and address of the person recovering the tag.

Sablefish possession and landing requirements

In the NSEI Subdistrict, the holder of a CFEC permit for sablefish may not retain more sablefish from the directed fishery than the annual amount of sablefish EQS specified by the department [5 AAC 28.170 (f)]. However, if a permit holder’s harvest exceeds the EQS for that year, by not more than 5%, ADF&G shall reduce the permit holder’s EQS for the following year by the amount of the overage. If a permit holder’s harvest exceeds the permit holder’s EQS by more than 5%, the proceeds from the sale of the overage in excess of 5% shall be surrendered to the state and the permit holder may be prosecuted under AS 16.05.723 [5 AAC 28.170 (j)]. If a permit holder’s harvest is less than the permit holder’s EQS established for the year, ADF&G shall increase the permit holder’s PQS only for the following year by the amount of the underage that does not exceed 5% of the EQS [5 AAC 28.170 (k)]. For the 2023 fishing season, 5% of the annual EQS is 956.05 round pounds.

Fish ticket requirements

Landed weights must be recorded on a fish ticket at the time of delivery. If a fisherman delivers fish in the round, the total round weight delivered must be recorded on the fish ticket. If a fisherman delivers dressed fish, the fish ticket must include the total landed dressed weight as well as the round weight equivalent, determined by using the standard 0.63 recovery rate. There is a 2% allowance for ice and slime when unrinsed whole iced sablefish are weighed. A fish ticket must be completed prior to the resumption of fishing and each permit holder must retain, on board their vessel, copies of all NSEI sablefish tickets from the current season and their updated PQS tracking form. When delivering fish out of state, a completed fish ticket must be submitted to ADF&G prior to transporting fish out of Alaska.

Bycatch allowances for other species

Full retention and reporting of rockfish Sebastes, excluding thornyhead rockfish Sebastolobus, is required for internal waters (5 AAC 28.171). The full retention regulation does not apply to thornyhead rockfish at the time of publication but will when the new regulations become effective in 2022. The allowable bycatch that may be legally landed and sold on an NSEI sablefish permit is based on round weight of sablefish and bycatch species or species group on board the vessel:

  • All rockfish, including thornyheads: 15% in aggregate, of which 1% may be demersal shelf rockfish (DSR), which includes yelloweye, quillback, canary, tiger, copper, China, and rosethorn rockfish
  • Lingcod: 0%
  • Pacific cod: 20%
  • Spiny dogfish: 35%
  • Other groundfish: 20%

All rockfish retained in excess of allowable bycatch limits shall be reported as bycatch overage on an ADF&G fish ticket. All proceeds from the sale of excess rockfish bycatch shall be surrendered to the state. Excess rockfish retained due to full retention requirements may be retained for personal use; however, the pounds must be documented as overage on the fish ticket.

A CFEC permit holder fishing for groundfish must retain all Pacific cod when the directed fishery for Pacific cod is open and up to the maximum retainable bycatch amount (20%) of Pacific cod when a directed fishery for Pacific cod is closed [5 AAC 28.070 (e)]. Pacific cod taken in excess of the bycatch limit in areas open to directed fishing for Pacific cod may be landed on a CFEC miscellaneous saltwater finfish permit designated for the gear that was used. Fishermen with halibut Individual Fishing Quota (IFQ) in regulatory area 2C and a CFEC halibut permit card must retain all halibut over 32 inches in length, up to the amount of their IFQ.

Sablefish live market

The holder of a CFEC or interim use permit for sablefish may possess live sablefish for delivery as live product except that, upon request of a local representative of the department or law enforcement, a permit holder must present sablefish for inspection and allow biological samples to be taken [5 AAC 28.170 (l)].

Prohibitions

The operator of a fishing vessel may not take sablefish in the NSEI area with sablefish from another area on board. Also, the operator of a vessel taking sablefish in the NSEI area shall unload those sablefish before taking sablefish in another area [5 AAC 28.170(a) and (b)].

A vessel, or person onboard a vessel, from which commercial, subsistence, or personal use longline fishing gear was used to take fish in the NSEI or SSEI Subdistricts during the 72-hour period immediately before the start of the commercial sablefish fishery in that subdistrict, or from which that gear will be used during the 24-hour period immediately after the closure of the commercial sablefish fishery in that subdistrict, may not participate in the taking of sablefish in that subdistrict during that open sablefish fishing period. A vessel, or a person onboard a vessel, who has harvested and sold their personal quota share before the final day of the sablefish season in that subdistrict is exempt from the prohibition on fishing longline gear during the 24-hour period immediately following the closure of the sablefish fishery in that subdistrict. In addition, a vessel or a person on board a vessel commercial fishing for sablefish in the NSEI Subdistrict may not operate subsistence or personal use longline gear for groundfish from that vessel until all sablefish harvested in the commercial fishery are offloaded from the vessel.


FUTURE WORK AND RECOMENDATIONS

These tasks are viewed as the next steps in developing the SCAA:

  1. It is expected that participation in the pot fishery in 2023 will increase dramatically as it has in the SSEI and the federal fishery where pots have been legal for several years. This will need to be monitored closely to see how catch rates and fish size varies between the longline and pot fisheries. This issue will involve significant model development and will be of primary concern as the fleet changes fishing practices.
  2. Develop methods to estimate fishery selectivity as this will make the model less dependent on federal values and the assumption that selectivity in the federal fishery mirrors that in the NSEI fishery. Initial efforts to do this failed to produce converged numbers and reasonable estimates of selectivity. Exploring the use of priors on the selectivity parameters, based on the federal estimates, may be an option. Exploring time varying selectivity in both the fishery and the survey may also provide options that could improve the fit of age and length data.
  3. Review the mark-recapture analysis for two primary reasons:
    1. Determine if less biased estimates of abundance can be produced and by modelling size and geographic differences in capture probabilities, and
    2. Determine the level of bias in the abundance estimates by comparing recapture rates between the longline survey and the fishery
  4. Continue to develop proper data weighting for the model by
    1. using estimated uncertainty in the indices and allowing the model to estimate extra-uncertainty parameters, and
    2. continuing to develop the Dirichlet data weighting of the age and length composition data.
  5. Implement the SCAA model in a Bayesian framework. Preliminary work has been done using the R library tmbstan (Monnahan and Kristensen 2018). The process is currently very slow; the next steps include optimizing the NUTS algorithm using methods detailed in the supplementary material of Monnahan and Kristensen (2018).

ACKNOWLEDGEMENTS

Many thanks to ADF&G Region I Groundfish Project staff who have collected NSEI sablefish data, maintained documentation, and worked to improve the conservation and management of this unique fishery. Additionally, we would like to thank the Age Determination Unit staff, including Kevin McNeel, Chris Hinds, and Catherine Mattson, who provide age data in a timely manner for stock assessments. We are grateful to Region I analyst/programmers, Karl Wood and Justin Daily, who provide database support and application development. Thans to Jane Sullivan, the original author of this model, who continues to offer insight and advice in developing this assessment. We also wish to thank Curry Cunningham and his graduate student Matt Cheng with the University of Alaska Fairbanks, College of Fisheries and Ocean Science for their advice in developing this model. Finally, we are thankful to the NOAA scientists for their continued collaborations and sharing their sablefish knowledge.

REFERENCES

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TABLES




Table 1: Annual harvest objective (round lb), equal quota share (round lb), reported harvest (round lb), exvessel value, numberof permits, and effort (dats) for the directed commercial Northern Southeast Inside (NSEI) Subdistrict sablefish fishery, 1985-2022.
Year Annual harvest objective Equal quota share Harvest Exvessel value (mil) No. of permits No. of days
1985 2,380,952 NA 2,951,056 $2 105 3
1986 2,380,952 NA 3,874,269 $2.9 138 2
1987 2,380,952 NA 3,861,546 $3.4 158 1
1988 2,380,952 NA 4,196,601 $4.4 149 1
1989 2,380,952 NA 3,767,518 $3.5 151 1
1990 2,380,952 NA 3,254,262 $3.1 120 1
1991 2,380,952 NA 3,955,189 $5.5 127 1
1992 2,380,952 NA 4,267,781 $5.4 115 1
1993 2,380,952 NA 5,795,974 $6.6 120 1
1994 4,761,905 38,889 4,708,584 $8.1 121 30
1995 4,761,905 38,889 4,543,272 $9 121 30
1996 4,761,905 38,889 4,676,032 $10.1 122 61
1997 4,800,000 39,300 4,752,285 $12.2 122 76
1998 4,800,000 41,700 4,689,713 $7.4 116 76
1999 3,120,000 28,000 3,043,272 $6.5 112 76
2000 3,120,000 28,600 3,081,797 $8.6 111 76
2001 2,184,000 19,600 2,142,619 $4.6 111 76
2002 2,005,000 18,400 2,009,379 $5.3 109 76
2003 2,005,000 18,565 2,003,083 $4.8 108 93
2004 2,245,000 20,787 2,230,396 $4.6 108 93
2005 2,053,000 19,400 2,027,187 $5 106 93
2006 2,053,000 19,550 2,031,227 $5.1 105 93
2007 1,488,000 14,500 1,501,483 $3.7 103 93
2008 1,508,000 15,710 1,513,043 $4.4 96 93
2009 1,071,000 12,170 1,069,217 $3.3 88 93
2010 1,063,000 12,218 1,054,279 $3.8 87 93
2011 880,000 10,602 882,777 $4.4 83 93
2012 975,000 12,342 969,775 $3.9 79 93
2013 1,002,162 12,848 972,740 $2.6 78 93
2014 745,774 9,561 773,534 $2.7 78 93
2015 786,748 10,087 781,702 $3.1 78 93
2016 650,754 8,343 646,329 $2.8 78 93
2017 720,250 9,234 714,404 $3.6 78 93
2018 855,416 10,967 855,600 $4.2 78 93
2019 920,093 11,796 909,341 $4 78 93
2020 1,108,003 14,773 1,101,091 $3.1 75 93
2021 1,137,867 15,587 1,083,363 $2.8 73 93
2022 1,233,633 16,899 1,182,518 $3.6 71 93
2023 1,395,686 19,121 NA $NA NA 93




Table 2: Summary of key assessment results used to inform management in 2022 and 2023. The table includes the estimates of projected biomass (sablefish aged 2 years and above) and female spawning stock biomass, estimated biological reference points of unfished female spawning biomass (\(SB_{100}\)), female spawning bioass at 50% of unfished levels (\(SB_{50}\)), and the maximum target fishing mortality of \(F_{50}\). Additional values include the maximum permissible Acceptable Biological Catch (max ABC) defined by \(F_{50}\), the estimates of mortality from fishery releases that would result under max ABC and a discard mortality rate of 016, and the recommended ABC under the max 15% change management proceedure
Quantity/Status 2022 2023
Projected age-2 biomass (lb) 51,885,665 51,975,426
Projected female spawning biomass (lb) 19,714,244 19,836,111
Unfished female spawning biomass (\(SB_{100}\), lb) 28,995,917 28,434,171
Equilibrium female spawning biomass (\(SB_{50}\), lb) 14,497,958 14,217,085
max \(F_{ABC}\) = \(F_{50}\) 0.062 0.059
Recommended \(F_{ABC}\) 0.056 0.059
Mortality from fishery discards under max ABC (lb) 72,190 69,522
Max ABC (lb) 1,595,932 1,486,406
Recommended ABC (lb) 1,443,314 1,573,109




Table 3: Decrement types and amounts, 2018-2023. Estimated catch in round pounds of sablefish.
Year 2018 2019 2020 2021 2022 2023
Acceptable biological catch 965,354 1,058,037 1,216,743 1,255,056 1,443,314 1,573,109
Decrement Type (round lb) Estimated Mortality
Bycatch mortality in halibut fishery\(^a\) 19,583 18,434 16,207 38,124 35,406 35,445
ADF&G longline survey removal decrement (excluding catch retained by permit holders for their equal quota share\()^a\) 15,875 26,260 24,698 42,499 95,502 75,636
Guided sport fish harvest\(^b\) 41,179 33,135 35,004 753 33,990 34,395
Unguided sport fish harvest\(^b\) 5,872 11,340 5,280 5,631 9,846 2,655
Mortality from fishery deadloss\(^a\) 5,699 8,046 9,729 10,888 11,085 9,467
Mortality from fishery releases\(^a\) 19,142
Subsistence and personal use harvest\(^b\) 21,730 21,587 17,821 19,295 23,852 18,643
Total decrements 109,938 137,944 108,740 117,189 209,681 177,241
Annual harvest objective 855,416 920,093 1,108,003 1,137,867 1,233,633 1,395,868
Permit holders 78 78 75 73 73 73
Equal quota share 10,967 11,796 14,773 15,587 16,899 19,121
a Projected estimate of mortality for the current season.
b Estimate of mortality that occurred during the previous season and is applied as decrement for the current season.




Table 4: A comparison for biological reference points from candidate models in the 2023 assessment. The base model refers to the model used in the prior assessment. The ‘tuned’ model refers to the base model with age and length compositions tuned via McAllister and Ianelli (1997) methodology. Progression from that model adds the updated fishery selectivity curves from the federal assessment while v23 model modifications are described in this document. The v23 no MR 5 and 10 refer to models where mark-recapture abundance estimates were dropped in the last 5 and last 10 years, respectively.
Base Tuned base Tuned base w/ new selectivity v23 v23 no MR in last 5 yrs v23 no MR in last 10 yrs
Number of parameters: 136 136 136 146 146 146
Negative log likelihood: 2,396 2,396 6,919 1,799 1,791 1,747
Maximum gradient component: 1.83e-06 1.40e-10 6.66e-12 3.32e-12 1.59e-07 1.54e-11
Projected age-2 biomass: 61,145,122 71,385,368 66,676,302 51,975,427 52,424,435 57,371,915
Projected female spawning biomass: 23,441,266 27,128,399 26,271,709 19,836,112 20,020,673 22,208,439
Unfished equilibrium female spawning biomass (SPR = 100): 30,866,389 32,930,727 33,033,358 28,434,171 28,527,598 30,309,066
Equilibrium female spawning biomass under\(F_{50}\) (SPR = 50): 15,433,194 16,465,363 16,516,679 14,217,086 14,263,799 15,154,533
Max ABC: 1,873,598 2,152,761 1,983,085 1,486,406 1,499,490 1,666,358
Recommended ABC: 1,659,811 1,659,811 1,659,811 1,486,406 1,499,490 1,659,811
Mortality from fishery discards under max ABC: 79,711 91,383 82,775 69,522 70,182 75,426
max \(F_{ABC}\) = \(F_{50}\): 0.063 0.0626 0.059 0.0591 0.0591 0.059
F under recommended ABC: 0.056 0.0483 0.049 0.0591 0.0591 0.0588




Table 5: Variable definitions for the statistical catch-at-age model.
Variable Definition
\(\textit{Indexing and model dimensions}\)
\(T\) Number of years in the model
\(t\) Index for year in model equations
\(A\) Number of ages in the model
\(a\) Index for age in model equations
\(a_0\) Recruitment age (age-2)
\(a_{+}\) Plus group age (age-31)
\(l\) Index for length bin in model equations
\(l_0\) Recruitment length bin (41 cm)
\(l_{+}\) Plus group length bin (99 cm)
\(fsh\) NSEI longline fishery
\(srv\) ADF&G longline survey
\(MR\) Mark-recapture abundance
\(\textit{Parameters}\)
\(M\) Instantaneous natural mortality
\(F\) Instantaneous fishing mortality
\(Z\) Total instantaneous mortality
\(S\) Total annual survival
\(D\) Discard mortality
\(s_{50}\) Age at which 50% of individuals are selected to the gear
\(s_{95}\) Age at which 95% of individuals are selected to the gear
\(\delta\) Slope parameter in the logistic selectivity curve
\(q\) Catchability
\(\mu_R\) Mean log recruitment
\(\tau_t\) Log recruitment deviations
\(\mu_N\) Mean log initial numbers-at-age
\(\psi_a\) Log deviations of initial numbers-at-age
\(\sigma_R\) Variability in recruitment and initial numbers-at-age
\(\mu_F\) Mean log fishing mortality
\(\phi_t\) Log fishing mortality deviations
\(\theta\) Dirichlet-multinomial parameter related to effective sample size
\(\textit{Data and predicted variables}\)
\(w_a\) Weight-at-age
\(p_a\) Proportion mature-at-age
\(r_a\) Proportion female-at-age
\(R\) Retention probability
\(s_a\) Selectivity-at-age
\(\Omega_{a',a}\) Ageing error matrix (proportion observed at age given the true age \(a'\))
\(\Lambda_{a,l,k}\) Age-length key (proportion in length bin given age and sex)
\(N\) Numbers-at-age
\(C\) Landed catch in numbers-at-age
\(I\), \(\hat{I}\) Indices of abundance, \(\hat{I}\) are predicted values
\(P_a\), \(\hat{P}_a\) Age compositions, \(\hat{P}_a\) are predicted values
\(P_l\), \(\hat{P}_l\) Length compositions, \(\hat{P}_l\) are predicted values
\(Y\), \(\hat{Y}\) Landed catch biomass, \(\hat{Y}\) are predicted values
\(\hat{W}\) Estimated mortality from discards (biomass)
\(\lambda\) Weight for likelihood component
\(L\) Likelihood
\(\omega\) Effective sample size for age and length compositions
\(n\) Input sample size for Dirichlet-multinomial likelihood
\(c\) Small constant (0.00001)




Table 6: A summary of data inputs to the mark-recapture models, including total individuals tagged (K), the total number of tags remaining once size selectivity is accounted for (\(K_0\)), tags not available to the longline survey or fishery (captured in ther fisheries or outside Chatham, \(D_0\)), recaptured individuals in the longline survey and fishery (\(k_{srv}\) and \(k_{fsh}\)), number of sampled individuals in the longline survey and fishery (\(n_{srv}\) and \(n_{fsh}\)), tags not available to the fishery (captured outside Chatham or in other fisheries during the survey, \(D_{srv}\), and tags recaptured in other fisheries or outside Chatham during the fishery (\(D_{fsh}\)) for years with a tagging survey, 2005-2023.
Year \(K\) \(K_0\) \(D_0\) \(k_{srv}\) \(n_{srv}\) \(D_{srv}\) \(k_{fsh}\) \(n_{fsh}\) \(D_{fsh}\)
2005 7,118 7,118 9 0 0 104 690 180,999 189
2006 5,325 5,325 3 0 0 46 503 203,878 123
2007 6,158 6,055 2 0 0 43 335 150,729 77
2008 5,450 5,412 4 40 15,319 54 431 156,313 104
2009 7,071 7,054 7 0 0 51 285 105,709 92
2010 7,443 7,307 4 54 14,765 60 331 106,201 38
2012 7,582 7,548 23 0 0 70 380 97,134 72
2013 7,961 7,921 24 0 0 89 374 99,286 113
2015 6,862 6,765 1 0 0 73 242 70,273 49
2017 7,096 6,933 3 0 0 42 197 60,409 11
2018 9,678 9,160 13 0 0 77 183 65,940 142
2019 11,094 10,208 6 0 0 51 201 71,044 122
2020 7,916 7,824 6 0 0 75 240 103,190 129
2022 8,654 8,638 8 46 22,745 62 334 162,074 233
Table 7: Assumed selectivity parameters for the fishery before the Equal Quota Share program started in 1994 (pre-EQS) and the fishery since the implementation of EQS for females (black points) and males (grey triangles). These parameters estimates were borrowed from the Federal stock assessment, where the Federal derby fishery and IFQ fishery were assumed to represent pre-EQS and EQS NSEI fisheries.
Male
Female
\(s_{50}\) \(\delta_{50}\) \(s_{50}\) \(\delta_{50}\)
Pre-EQS Fishery 7.27 0.49 3.82 0.49
EQS Fishery 4.29 0.90 3.34 1.76




Table 8: Parameter estimates from the statistical catch-at-age model. Estimates of recruitment, initial numbers-at-age, and fishing mortality deviations were excluded for brevity.
Parameter Estimate Lower 95% CI Upper 95% CI
Survey male selectivity pre-2000, \(\mbox{s}_{50}\) 6.237 4.161 10.307
Survey male selectivity 2000-2022, \(\mbox{s}_{50}\) 5.042 4.511 5.685
Survey male selectivity pre-2000, \(\delta\) 0.562 0.243 1.300
Survey male selectivity 2000-2022, \(\delta\) 0.802 0.613 1.050
Survey female selectivity pre-2000, \(\mbox{s}_{50}\) 3.896 3.261 4.849
Survey female selectivity 2000-2022, \(\mbox{s}_{50}\) 3.697 3.493 3.928
Survey female selectivity pre-2000, \(\delta\) 1.525 0.732 3.177
Survey female selectivity 2000-2022, \(\delta\) 2.348 1.649 3.345
Pre-EQS catchability, \(\mbox{ln}(q_{fsh,pre-EQS})\) -17.670 -17.751 -17.589
EQS catchability, \(\mbox{ln}(q_{fsh,EQS})\) -17.243 -17.292 -17.193
Survey catchability pre-2000, \(\mbox{ln}(q_{srv})\) -16.880 -17.003 -16.758
Survey catchability 2000-2022, \(\mbox{ln}(q_{srv})\) -16.718 -16.777 -16.658
Mark-recapture catchability, \(\mbox{ln}(q_{MR})\) -0.043 -0.062 -0.024
Mean recruitment, \(\mu_R\) 799,173 669,879 953,423
Mean initial numbers-at-age, \(\mu_N\) 1,020,153 776,952 1,339,481
Variability in recruitment and initial numbers-at-age (random effects parameter), \(\sigma_R\) 0.521 0.439 0.618
Mean fishing mortality, \(\mu_F\) 0.056 0.030 0.106
Table 9: Negative likelihood values and percent of each component to the total likelihood. The data likelihood is the sum of all likelihood contributions from data. The difference between the total likelihood and the data likelihood is the contribution of penalized likelihoods, including recruitment and fishing mortality.
Likelihood component \(NLL\) % of \(NLL\)
Catch 17.6 1.0
Fishery CPUE 178.9 9.9
Survey CPUE 107.7 6.0
Mark-recapture abundance 84.9 4.7
Fishery ages 228.9 12.7
Survey ages 274.0 15.2
Fishery lengths 368.3 20.5
Survey lengths 539.8 30.0
Data likelihood 1800.1 100.0
Fishing mortality penalty 1.4 0.1
Recruitment likelihood -11.7 -0.6
SPR penalty 0.0 0.0
Sum of catchability priors 9.1 0.5
Total likelihood 1798.9 99.9




FIGURES




Northern Southeast Inside (NSEI) and Southern Southeast Inside (SSEI) Subdistricts including restricted waters of Glacier Bay National Park and Preserve and Annette Islands Reserve.

Figure 1: Northern Southeast Inside (NSEI) and Southern Southeast Inside (SSEI) Subdistricts including restricted waters of Glacier Bay National Park and Preserve and Annette Islands Reserve.




Catch, landings by port, and ex-vessel value for Northern Southeast Inside (NSEI) Subdistrict commercial sablefish 1985-2022.

Figure 2: Catch, landings by port, and ex-vessel value for Northern Southeast Inside (NSEI) Subdistrict commercial sablefish 1985-2022.




Estimated catch in the NSEI fishery from 2000 - 2022 and the relationship to $F_{40}$, $F_{50}$ and $F_{60}$ (Fspr), the fishing mortality that results in a spawner-per-recruit (SPR) of 40, 50 and 60% of the population's virgin state, in the base model and model v23. Note that model v23, which makes fewer assumptions based on the federal assessment and is more dpendent on NSEI data, estimates the population as much closer to the ADF&G management target of $F_{50}$.

Figure 3: Estimated catch in the NSEI fishery from 2000 - 2022 and the relationship to \(F_{40}\), \(F_{50}\) and \(F_{60}\) (Fspr), the fishing mortality that results in a spawner-per-recruit (SPR) of 40, 50 and 60% of the population’s virgin state, in the base model and model v23. Note that model v23, which makes fewer assumptions based on the federal assessment and is more dpendent on NSEI data, estimates the population as much closer to the ADF&G management target of \(F_{50}\).




A summary of the available data sources in NSEI by year.

Figure 4: A summary of the available data sources in NSEI by year.




A comparison of the mean length and age in the longline fishery and longline survey since 1997 for male and female sablefish in the NSEI district.

Figure 5: A comparison of the mean length and age in the longline fishery and longline survey since 1997 for male and female sablefish in the NSEI district.




Biological inputs to the statistical catch-at-age model, including: (A) von Bertalanffy growth model predictions of weight-at-age (kg) by sex from the longline fishery (black) and ADFG longline survey (grey); (B) proportion mature at age for females estimated from the longline survey with the age at 50% maturity ($a_{50}$=6.4 yr); and (C) proportion female in the longline survey, where the curve is the fitted line from a generalized additive model +/- 2 standard error.

Figure 6: Biological inputs to the statistical catch-at-age model, including: (A) von Bertalanffy growth model predictions of weight-at-age (kg) by sex from the longline fishery (black) and ADFG longline survey (grey); (B) proportion mature at age for females estimated from the longline survey with the age at 50% maturity (\(a_{50}\)=6.4 yr); and (C) proportion female in the longline survey, where the curve is the fitted line from a generalized additive model +/- 2 standard error.




Changes in length- and maturity-at-age over time in the NSEI sablefish population. There is a general trend of fish maturing at younger ages and smaller sizes. The model uses an average of all years for the assessment.Changes in length- and maturity-at-age over time in the NSEI sablefish population. There is a general trend of fish maturing at younger ages and smaller sizes. The model uses an average of all years for the assessment.

Figure 7: Changes in length- and maturity-at-age over time in the NSEI sablefish population. There is a general trend of fish maturing at younger ages and smaller sizes. The model uses an average of all years for the assessment.




Indices of catch and abundance with the assumed error distribution, including: (A) harvest (round mt), (B) fishery catch per unit effort in round kg per hook, (C) survey catch per unit effort in number of fish per hook, and (D) mark-recapture abundance estimates in millions. The dashed vertical line in 1994 mark the transition to the Equal Quota Share program.

Figure 8: Indices of catch and abundance with the assumed error distribution, including: (A) harvest (round mt), (B) fishery catch per unit effort in round kg per hook, (C) survey catch per unit effort in number of fish per hook, and (D) mark-recapture abundance estimates in millions. The dashed vertical line in 1994 mark the transition to the Equal Quota Share program.




CPUE in the NSEI longline sablefish fishery in round lbs per hook. The nominal values (blue) represent values from past assessments and the fully standardized values represent the values used in this assessment.

Figure 9: CPUE in the NSEI longline sablefish fishery in round lbs per hook. The nominal values (blue) represent values from past assessments and the fully standardized values represent the values used in this assessment.




Proportions-at-age for in the NSEI longline fishery (2002-2022) and ADFG longline survey (1997-2022).

Figure 10: Proportions-at-age for in the NSEI longline fishery (2002-2022) and ADFG longline survey (1997-2022).




Longline fishery and survey length distributions by sex from 1997-2022.

Figure 11: Longline fishery and survey length distributions by sex from 1997-2022.







The probability of retaining a fish as a function of weight (left), sex, and age (right).

Figure 12: The probability of retaining a fish as a function of weight (left), sex, and age (right).




Fixed age-based selectivity curves for the fishery before the Equal Quota Share program started in 1994 (pre-EQS), the fishery since the implementation of EQS, and the estimated ADFG longline survey for females (black points) and males (grey triangles) before and after the standardization of the survey in 2000. Fishery selectivity parameter estimates were borrowed from the Federal stock assessment for the derby fishery (pre-EQS) and IFQ fishery (EQS), while the survey selectivity parameters are estimated within the model.

Figure 13: Fixed age-based selectivity curves for the fishery before the Equal Quota Share program started in 1994 (pre-EQS), the fishery since the implementation of EQS, and the estimated ADFG longline survey for females (black points) and males (grey triangles) before and after the standardization of the survey in 2000. Fishery selectivity parameter estimates were borrowed from the Federal stock assessment for the derby fishery (pre-EQS) and IFQ fishery (EQS), while the survey selectivity parameters are estimated within the model.




Fits to indices of catch and abundance with the assumed error distribution shown as shaded grey polygons. Input data are shown as grey points and model fits are shown in black. Indices include (A) harvest (round mt); (B) fishery catch per unit effort in round kg per hook with separate selectivity and catchability time periods before and after the implementation of the Equal Quota Share program in 1994; (C) survey catch per unit effort in number of fish per hook; and (D) mark-recapture abundance estimates in millions. Solid and dashed lines in panel D reflect years for which data were and were not available, respectively.

Figure 14: Fits to indices of catch and abundance with the assumed error distribution shown as shaded grey polygons. Input data are shown as grey points and model fits are shown in black. Indices include (A) harvest (round mt); (B) fishery catch per unit effort in round kg per hook with separate selectivity and catchability time periods before and after the implementation of the Equal Quota Share program in 1994; (C) survey catch per unit effort in number of fish per hook; and (D) mark-recapture abundance estimates in millions. Solid and dashed lines in panel D reflect years for which data were and were not available, respectively.




Model predictions of (A) age-2 recruitment (millions), (B) female spawning stack biomass (million lb), (C) exploitable abundance (millions), and (D) exploitable biomass (million lb).

Figure 15: Model predictions of (A) age-2 recruitment (millions), (B) female spawning stack biomass (million lb), (C) exploitable abundance (millions), and (D) exploitable biomass (million lb).




Fits to fishery age compositions, 2002-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.

Figure 16: Fits to fishery age compositions, 2002-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.




Fits to survey age compositions, 1997-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.

Figure 17: Fits to survey age compositions, 1997-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.




Standardized residuals of fits to fishery (2002-2022) and survey (1997-2022) age compositions. Size of residual scales to point size. Black points represent negative residuals (observed < predicted); white points represent positive residuals (observed > predicted).

Figure 18: Standardized residuals of fits to fishery (2002-2022) and survey (1997-2022) age compositions. Size of residual scales to point size. Black points represent negative residuals (observed < predicted); white points represent positive residuals (observed > predicted).




Fits to male fishery length compositions, 2002-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.

Figure 19: Fits to male fishery length compositions, 2002-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.




Fits to female fishery length compositions, 2002-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.

Figure 20: Fits to female fishery length compositions, 2002-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.




Fits to male survey length compositions, 1997-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.

Figure 21: Fits to male survey length compositions, 1997-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.




Fits to female survey length compositions, 1997-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.

Figure 22: Fits to female survey length compositions, 1997-2022. Observed and predicted proportions-at-age shown as grey bars and black lines, respectively.




Standardized residuals of fits to fishery (2002-2022) and survey (1997-2022) length compositions for males and females. Size of residual scales to point size. Black points represent negative residuals (observed < predicted); white points represent positive residuals (observed > predicted).

Figure 23: Standardized residuals of fits to fishery (2002-2022) and survey (1997-2022) length compositions for males and females. Size of residual scales to point size. Black points represent negative residuals (observed < predicted); white points represent positive residuals (observed > predicted).




Mohn's $\rho$ and retrospective peels of sablefish spawning biomass for the last 9 years.

Figure 24: Mohn’s \(\rho\) and retrospective peels of sablefish spawning biomass for the last 9 years.




Mohn's $\rho$ and retrospective peels of sablefish recruitment for the last 9 years.

Figure 25: Mohn’s \(\rho\) and retrospective peels of sablefish recruitment for the last 9 years.




Model-estimated fishing mortality rate (top) and realized harvest rate (bottom), defined as the ratio of total predicted catch to exploitable biomass. Total predicted catch is the sum of landed catch and discarded biomass assumed to die post-release.

Figure 26: Model-estimated fishing mortality rate (top) and realized harvest rate (bottom), defined as the ratio of total predicted catch to exploitable biomass. Total predicted catch is the sum of landed catch and discarded biomass assumed to die post-release.













#```{r ageerror, fig.cap= paste0(“Ageing error matrix used in the model, showing the probability of #observing an age given the true #age (Heifetz et al. 1999).”)}

#knitr::include_graphics(paste0(“../figures/tmb/ageing_error.png”)) #```

#```{r srvlen, fig.cap= paste0(“Longline survey length distributions by sex from 2012-”,YEAR,“. Vertical #bars represent the data nd the black line shows the length composition from the most recent year #superimposed on previous years.”)}

#knitr::include_graphics(paste0(figures_dir,“/llsrv_lencomps_2012_”,YEAR,“.png”), rel_path=FALSE) #```

#```{r agelenkey, fig.cap= paste0(“Age-length key used in the model, with the relative size of the #bubbles reflecting the probability #that a fish of a given age falls within a certain length bin (Echave #et al. 2012). The probabilities sum to 1 across each age.”)}

#knitr::include_graphics(paste0(“../figures/tmb/age_length_key.png”)) #```

#```{r residabdind, fig.cap= paste0(“Standardized residuals of fits to indices of catch and abundance, #including: (A) harvest, (B) #fishery catch per unit effort, (C) survey catch per unit effort, and (D) #mark-recapture (MR) abundance.”)}

#knitr::include_graphics(paste0(tmb_mod_figures_dir,“/selectivity_”,YEAR,“.png”)) #knitr::include_graphics(paste0(“../figures/tmb/presid_abd_indices.png”)) #```

  1. Alaska Department of Fish and Game, Commercial Fisheries Division, Juneau, Alaska↩︎

  2. Alaska Department of Fish and Game, Commercial Fisheries Division, Sitka, Alaska↩︎